My sister has a beautiful store bought hand knit sweater and I would like to try to replicate it (more or less). If i weigh her sweater, will that give me the true amount of yarn I would need? Or am I totally off track? Wouldn't you just assume that would work? And maybe add a little extra yarn just in case?

One thing to consider with the weight of yarn, is the different weight of different materials. Kind of like the difference between the weight of oil and water, or gold and wood.

I don't know how to estimate the necessary amount of yarn, but in order for the weight to give you the exact amount of yarn, the same materials, treatments, etc would need to be used. The yarn would need to be exactly the same in every way. If you are using yarn with the same wpi and fiber content I guess it could be close enough, though I would definately buy more to be sure.

When I typed "estimating yarn amount" into google, there looked to be a few promising pages, but as I haven't tried any of the methods, I can't recommend any.

If you've knit a sweater before, you may have an idea how much yardage it took. I'm finding that for a pullover I need about 800 yards of worsted weight on the needle sizes I generally use for sweaters. So it's basically figuring it out for you. Look at patterns that may be similar, out of similar yarn and see how much is needed for your size.

soozeq - yep I have knitted many sweaters these past few years... but as zeeblebee said before, I have to take into account the different weight of the yarn etc, so I don't want to just assume that because a pattern is similar, it's going to take the same amount of yarn.. know what I mean? I'm probably being fussy blah, blah, but I just don't want to get caught out! Oh and how much would 800 yards be in metres or grams? We don't really use yards that much where I live.

mistessmegan - that great! thanks so much - it will really come in handy.

Most patterns give the yards or meters required for a piece because yarns vary so much by weight. 50 grams might be 75 meters or 190. Most worsted weight is *about* 110 meters per 50 grams, but not always.

At least I'm getting a little closer to understanding how different weights etc. work.

I guess sometimes it's just trial and error with guessing how much yarn you really need for a project. Occasionally I get caught out with not enough yarn, even though the pattern calls for whatever they say you need, so who knows really.